1. Field of the Invention
Embodiments relate to semiconductor integrated circuit fabrication.
2. Background
A recent development in semiconductor processing is the tri-gate transistor. A tri-gate transistor includes a thin semiconductor body formed on a substrate. A gate dielectric is formed on the top surface and the sidewalls of the semiconductor body. A gate electrode is formed on the surface of the gate dielectric on the top surface and the sidewalls of the semiconductor body. Source and drain regions are formed in the semiconductor body on opposite sides of the gate electrode. Because the gate electrode and the gate dielectric surround the semiconductor body on three sides, the transistor essentially has three separate gates. These three separate gates provide three separate channels for electrical signals to travel, thus effectively tripling the conductivity as compared to a conventional planar transistor.
Another recent development in semiconductor processing is the one-transistor (1-T) floating body cell (FBC), which may be used in an embedded memory. Conventional dynamic random access memory (DRAM) requires a transistor and a separator capacitor to implement a memory cell. The 1-T FBC stores a signal charge inside a floating body region, which modulates the threshold voltage of the transistor. As a result, the separate capacitor of the DRAM memory cell can be eliminated, thereby resulting in reduced cell area and higher density.
The 1-T FBC may be further optimized by a dual-gate structure. A dual-gate memory cell has two gates disposed on opposite sides of a silicon body, each gate being independently controlled. A gate dielectric is formed on two sides of the silicon body. Two gates are formed on the surface of the gate dielectric, one on each side of the silicon body. An insulating layer electrically isolates the gates from the top of silicon body. Because the dual gate device has a gate on each side of the channel, thickness of the silicon body can be double that of a single gate device and still obtain a fully depleted transistor operation.